The present invention relates to a printing method and a printing apparatus for filling a printing material into openings of a printing face of a body to be printed, and more particularly, to a printing method and a printing apparatus for applying paste, and to an apparatus for manufacturing circuit boards for electronic devices, etc.
Recently, circuit boards have been changed from single-face boards having circuits formed on one face, to double-face boards and multilayer circuit boards so as to achieve compact and high-performance apparatuses. Many of the boards adopted at present are advanced multilayered ones. In the meantime, a printing technique using a filling head, i.e., a squeegee is employed in order to press and fill a paste into openings such as via holes or through holes in these circuit boards, or to press and fill the paste into openings of a metal mask to form circuits on the board. A lot of conditions are involved in the printing technique, for instance, hardness of the squeegee, angle of the squeegee to a printing face, pressure of the squeegee to the printing face, filling speed of the squeegee to the openings of the printing face, etc. Even a slight error in setting of the conditions adversely influences the quality of printing films, and therefore the set conditions are adjusted based on experiences on the production line, thereby improving yields in the paste filling process and quality of products.
Some adaptations are also made to the aforementioned squeegee in the filling process. For example, the squeegee is improved in shape to have a flat, a sharp, or a curved contact face as the printing face. In one arrangement, a heater is built in the squeegee to heat the squeegee itself to a fixed temperature, thereby lowering a viscosity of the paste and increasing filling efficiency for the paste to the openings of the printing face.
The viscosity of the paste increases in proportion to an operating time of the squeegee. For stabilizing the viscosity, therefore, the paste is exchanged at a fixed time interval, or an organic solvent is added to the paste to adjust the viscosity.
Meanwhile, the amount of the paste filled into the openings, e.g., via holes and through holes, etc. or the openings of the metal mask is controlled and stabilized by filling the paste up to a surface of the openings.
An example of the conventional circuit board-manufacturing method will be described with reference to FIGS. 13A, 13B.
FIGS. 13A, 13B respectively represent examples of a manufacturing method and a manufacturing apparatus for circuit boards in the filling process according to the conventional art.
In FIGS. 13A, 13B, 300 denotes a metal mask placed on a base material 301. 303 and 305 denote squeegees which move on the metal mask 300 while keeping touch with the metal mask 300. 304 denotes a paste, and 302 denotes a stage. The base material 301 is disposed in touch with on the stage 302. The metal mask 300 is arranged with a slight space above the base material 301, onto which the paste 304 is supplied. The squeegees 303, 305 located above the metal mask 300 can move in an up/down direction and in a printing direction of the squeegees 303, 305.
The paste is filled in the thus-constructed apparatus in a process described herein. The base material 301 is first set at a predetermined position on the stage 302. A through hole 301a formed in the base material 301 is registered with a hole 300a formed in the metal mask 300, and the metal mask 300 is set above the base material 301. The paste 304 is supplied onto the metal mask 300. The squeegees 303, 305 are lowered to hold the base material 301 by pressing a predetermined pressure on to the material 301. Thereafter, the squeegees 303, 305 are moved in the printing direction to move the paste 304 on the metal mask 300, thereby printing onto the base material 301. The paste 304 is pressed and filled in the through holes 301a formed in the base material 301 in this manner.
In the above paste filling process in the conventional art, a filling shape or the filling amount of the paste 304 is greatly changed even by mechanical errors, resulting in blanking, insufficient printing, or similar filling failures. When the flat squeegee 305 shown in FIG. 13B is used, a contact angle of the squeegee to the printing face of the metal mask 300 or base material 301 is hard to fix and maintain. The amount of the paste filled in the through hole 301a varies greatly and is considerably difficult to control properly. This is an important issue. In the case of the square squeegee 303 as shown in FIG. 13A, the contact angle of the squeegee to the printing face of the metal mask 300 or base material 301 is easy to set. A front end part of the square squeegee 303 in touch with the printing face of the base material 301 is not sufficiently sharp, and consequently the paste 304 is left on the metal mask 300 or base material 301. The front end part of the square squeegee can hold only a small amount of the paste 304. This makes it necessary to frequently replenish the paste 304, and thus deteriorates productivity. When a viscosity of the paste 304 is increased because of the evaporation of volatile components or when the paste of a high viscosity is used, considerably less paste is filled than if kept under the originally properly set conditions. In other words, the filling condition should be re-set during operation although this takes a long time. This is another issue. In the case where a heater is incorporated in the squeegee 303, 305, this arrangement merely lowers the viscosity of the paste 304. This does not effectively influence the rolling or filling of the paste 304 and raises the necessity for setting and adjusting the conditions again. Poor productivity still remains as an issue.
The object of the present invention is therefore to provide a printing method and a printing apparatus whereby a sufficient filling amount of a printing material into openings of a body to be printed is secured in conformity with various filling conditions, to thereby improve yields, quality, and productivity for printing with the printing material.
According to a first aspect of the present invention, there is provided a printing method for pressing and filling a printing material by means of a filling head to openings of a body to be printed, wherein a flow pressure of the printing material is kept roughly constant during printing of the printing material.
According to a second aspect of the present invention, at least either a contact angle of the filling head to a printing face of the body to be printed or the speed of the filling head can be changed in accordance with a change of the amount of the printing material in the above first aspect, thereby keeping the flow pressure of the printing material roughly constant.
According to a third aspect of the present invention, printing of the printing material can be conducted in the above first or second aspect while the filling head is supported at the side (first side) of a pressing face thereof in touch with the printing face of the body to be printed, thereby keeping the flow pressure of the printing material roughly constant.
According to a fourth aspect of the present invention, in any one of the above-described first-third aspects of the invention, a temperature gradient can be applied to the pressing face of the filling head so that a temperature of a part in touch with the printing face of the body to be printed is higher than that of a part away (second side) from the printing face of the body to be printed and the filling head, thereby keeping the flow pressure of the printing material roughly constant.
According to a fifth aspect of the present invention, in any one of the first through fourth aspects, a pretreatment material can be applied before the printing material is filled by the filling head into the openings at the printing face of the body to be printed, thereby keeping the flow pressure of the printing material roughly constant.
According to a sixth aspect of the present invention, there is provided a printing apparatus for pressing and filling a printing material by a filling head into openings of a body to be printed, which includes a holding device for keeping a flow pressure of the printing material roughly constant during printing of the printing material.
According to a seventh aspect of the present invention, the holding device in the sixth aspect can be a control part which changes at least either a contact angle of the filling head to a printing face of the body to be printed, or the speed of the filling head in accordance with a change of the amount of the printing material.
According to an eighth aspect of the present invention, the holding device in the seventh aspect can be a supporting member for supporting the filling head at the side of a pressing face thereof in touch with the printing face of the body to be printed.
According to a ninth aspect of the present invention, the holding device in any one of the sixth through eighth aspects can have a temperature-adjusting element which applies a temperature gradient to the pressing face of the filling head so that a temperature of a part in touch with the printing face of the body to be printed is higher than that of a part away from the printing face of the body to be printed and the filling head.
According to a tenth aspect of the present invention, the temperature-adjusting element in the ninth aspect can be adapted to set an optimal temperature gradient along the pressing face of the filling head from the side in touch with the printing face of the body to be printed.
According to an eleventh aspect of the present invention, the holding device in any one of the sixth through tenth aspects can have a pretreatment head for applying a pretreatment material to the filling head and the printing face of the body to be printed before the printing material is filled.
According to the present invention, during filling of the printing material, the flow pressure of the printing material is kept roughly constant, so that a sufficient filling amount of the printing material is secured into openings of the body to be printed in conformity with various filling conditions, thereby improving a yield, quality, and productivity of printing.
In the printing method and the printing apparatus of the above described aspects of the present invention, the filling head moves to press and fill. the printing material into openings of the base material or metal mask. At least either the contact angle of the filling head in relation to the printing face of the base material or metal mask, or the speed of the filling head is changed under a predetermined condition. For instance, a predetermined condition could be changing amount of the printing material as the filling head moves forward. Therefore, the flow pressure of the printing material is kept roughly constant to cope with an increase of a viscosity of the printing material with time or a decrease of the filling/pressing force due to the consumption of the printing material, etc. A predetermined amount of the printing material is stably secured at all times, thereby improving continuous printing efficiency.
According to the printing method and the printing apparatus of the further aspects of the present invention, the filling head is supported at the side of the pressing face thereof in touch with the printing face of the base material or metal mask. The side away from the printing face is rendered a free end and deformable, so that required flexibility is attained. The printing material is controlled so as to not leak when pressed by the filling head at the side in touch with the printing face. A necessary minimum elasticity is ensured for the filling head to trace the uneven printing face of the base material or metal mask. The flow pressure of the printing material is thus maintained roughly constant. A predetermined amount of the printing material is stably filled without any special control means against an increase of the viscosity of the printing material with time and reduction in volume of the printing material because of the consumption. Continuous printing efficiency can be improved.
In the printing method and the printing apparatus of the yet further aspect of the present invention, a predetermined temperature gradient is applied to the pressing face of the filling head. The temperature at the side of the pressing face in touch with the printing face is made high and the temperature decreases along the pressing face away from the printing face. As a result, the viscosity of the rolling printing material in touch with the printing face is lowered, thereby improving fluidity of the printing material and maintaining the nearly constant flow pressure of the printing material. At the same time, the temperature at the side of the pressing face away from the printing face is lower, whereby the fluidity is limited. Thereby hydraulic pressure of the pressing face of the part in touch with the printing face increases. Accordingly, not only a predetermined amount of the printing material is stably filled, but the evaporation of volatile components is restricted at the low temperature part. All of the printing material can be easily maintained at a predetermined viscosity, and continuous printing efficiency can be improved.
With the use of the temperature-adjusting element for applying the above-described temperature gradient, and when the temperature-adjusting element is constituted to set an optimal temperature gradient to a section of the pressing face away from the printing face of the base material or metal mask, circuit boards of various conditions can be manufactured with high quality in accordance with a variety of printing materials and filling conditions.
In the printing method and the printing apparatus of the different aspects of the present invention, in addition to the pressing and filling of the printing material by means of the filling head to openings of the base material or metal mask, the pretreatment head that is additionally provided is driven to apply the pretreatment material to the printing face of the base material or metal mask prior to the filling of the printing material. The effect of applying the nonvolatile organic substance can be achieved in one single filling process. If the pretreatment material, e.g., nonvolatile organic component. contained in the printing material is applied onto the body to be printed before the printing material is filled, an increase of the viscosity of the printing material can be suppressed. Thereby the flow pressure of the printing material. is maintained nearly constant and the continuous printing performance improves. Although the volatile component evaporates after the printing, the nonvolatile component adsorbs into the printing face which results in a change of a composition of the printing material. As such, the nonvolatile component is applied beforehand to prevent the change of the composition.